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# Permutations

As we have seen, the arrangements made by taking some or all elements out of a number of things is called a permutation. Permutation implies “arrangement” where “order of the things” is important.

The permutations of three things, a b and c, taken two at a time are ab, ba, ac, ca, cb and bc. Since the order in which the things are taken is important, ab and ba are counted as two different arrangements.

The number of permutations of n things taking r at a time is denoted by nPr.